Ulrike Grömping: Design of Experiments in R
This is a bit personal. I have very little (read "no") experience with designing experiments (DoE). Back in 2008 I met my wife's supervisor that was an author of an old commercial DoE software. We both realized that R missed a lot of DoE methods. The problem was my lack of theoretical knowledge in this area and his style of work. I gave up but I am happy that they finally finished the job without me - the book was published and the package is available on CRAN. Looking into DoE CRAN Task View - we were not alone.